Limited Partnership Interests in BGC Holdings and Newmark Holdings (Detail)		3 Months Ended	12 Months Ended
	Jul. 01, 2023 shares	Dec. 31, 2023 installment	Dec. 31, 2023 installment partnership
Noncontrolling Interest [Abstract]
Number of operating partnerships | partnership			2
Limited partnership interest, conversion ratio		1	1
Number of installment | installment		4	4
Quarterly percentage to preferred units		0.006875	0.006875
Percentage to preferred units			2.75%
Conversion of stock, shares converted (in shares)	64,000,000
Minimum number of shares required to be issued (in shares)	75,000,000
Newmark | Class A Common Stock
Noncontrolling Interest [Abstract]
Limited partnership interests exchange ratio			92.31%
Newmark Holdings
Noncontrolling Interest [Abstract]
Calculation of contribution ratio, denominator		2.2	2.2
Limited partnership interest, conversion ratio		1	1
BGC Holdings LPUs
Noncontrolling Interest [Abstract]
Limited partnership interest, conversion ratio		1	1